A current mirror is a device comprising an input, an output and a common terminal that is typically connected to a power supply or ground. The input may be connected to a current source. Ideally, the output current will then be equal to the input current and therefore the output is said to mirror the input current, thence the name. This should ideally be true for varying loads at the output.
Current mirrors comprised of active electronic circuit elements have been used extensively in analog electronic integrated circuits both as biasing elements and as load devices for amplifier stages. The use of current mirrors may frequently lead to decreased sensitivity to variations of parameters such as temperature or voltage supply. When the bias currents are small, it is often more economical to use current mirrors rather than resistors in order to save die area.
In modern integrated circuit design, current mirrors are often designed using Metal-Oxide Semiconductor Field Effect Transistors (MOSFETs). MOSFETs are normally assumed to have zero gate current. However, modern deep-submicron (fine geometry) Complementary MOS (CMOS) manufacturing processes result in small gate leakage currents through the thin oxide MOSFET devices. These deviations from theory can lead to significant change in the performance of current mirrors, which may ultimately affect the operation and functionality of integrated circuits comprising these current mirrors.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.